A random thought that has occurred to me as I’ve done a number of critiques in the last few months:
A lot of people say that grammar doesn’t matter because the editor fixes that anyway.
The voice of your book is shown in how the narrator uses grammar. Oh, a typo here or there isn’t going to make a difference–yes, copyeditors catch that.
But if there are so many spelling errors and comma splices and syntax errors that it’s impossible to make out just what the meaning of a sentence (or paragraph) is, you’re undermining the story you’re trying to communicate. Writing is all about communication, and to communicate well, grammar plays a vital role. It seems pretty basic to me that if you want to tell a story well, you need to know how to construct a sentence, a paragraph, a chapter, etc.
Just thought I’d throw that out there as something to think about. Grammar is part of your toolbox. Use it.